2.2 Major Divisions of Spectral Wavelength Regions
The wavelength of electromagnetic energy has such a wide range that no instrument can measure it completely. Different devices, however, can measure most of the major spectral regions.
The division of the spectral wavelength is based on the devices which can be used to observe particular types of energy, such as thermal, shortwave infrared and microwave energy. In reality, there are no real abrupt changes on the magnitude of the spectral energy. The spectrum are conventionally divided into various parts as shown below:
The optical region covers 0.3 - 15 mm where energy can be collected through lenses. The reflective region, 0.4 - 3.0 mm, is a subdivision of the optical region. In this spectral region, we collect solar energy reflected by the earth surface. Another subdivision of the optical spectral region is the thermal spectral range which is between 3 mm to 15 mm, where energy comes primarily from surface emittance. Table 2.1 lists major uses of some spectral wavelength regions.
Table 2.1. Major uses of some spectral wavelength regions
Detecting oil spill
Water depth, turbidity
3 cm - 15 cm
20 cm - 1 m
Water content in plant or soil
Mineral, rock types
Surface relief, soil moisture
Canopy penetration, woody biomass